The present invention relates to a plasma processing apparatus and method in which a plasma processing is performed for an object of processing such as a substrate.
A plasma processing apparatus is known as an apparatus for performing a processing for cleaning of a substrate surface on which electronic parts are to be mounted. In this plasma processing apparatus, a plasma discharge is generated in an evacuated vacuum chamber by applying a high-frequency voltage to a discharging electrode in the vacuum chamber after the introduction of a plasma generating gas into the vacuum chamber. A plasma processing for an object of processing placed on the discharging electrode is performed by the action of ions, electrons or the like generated by the plasma discharge.
In order to obtain an adequate processing effect by this plasma processing, it is necessary that a plasma processing condition such as the value of a high-frequency voltage applied to the discharging electrode should be set adequately in accordance with the object of processing. Hitherto, the setting of the plasma processing condition has been made on the basis of the result of a condition determining work performed for determining the optimum processing condition for each object of processing.
However, an effective electric power representing the action of the plasma discharge for plasma generation exerted on the object of processing differs depending upon the size, thickness and material of the object of processing. Therefore, in the case where a plasma processing is performed under the same condition, it is not possible to avoid the variations in quality of the plasma processing even in the case of similar objects of processing.
Also, at the time of operation of the plasma processing apparatus, removed substances attach to the inner wall of the vacuum chamber due to reverse sputtering so that a deposited layer is gradually formed on the inner wall of the vacuum chamber with the lapse of the operating time. This deposited layer causes a change in impedance of a plasma discharging circuit. Therefore, the effective electric power for the object of processing has a time dependent change even if a power supply output condition is kept constant. Accordingly, no adequate plasma processing condition is ensured resulting in that the variations in quality of the plasma processing are generated. Thus, the conventional plasma processing has a problem that owing to the difference between objects of processing and the time dependent change in internal state of the vacuum chamber, it is difficult to keep the adequate plasma processing condition.